Study of Kuo-type cumulus parameterizations during different epochs of the Asian summer monsoon

Abstract

The performances of several versions of the Kuo-type cumulus parameterization schemes have been examined during different phases of the summer monsoon. These phases are the preonset, an onset and a period of break in the monsoon. Special sets of upper air observations that were collected from stationary ships forming polygons over the Arabian Sea and the Bay of Bengal during MONEX-79 were used for this purpose. Cumulus warming, drying and precipitation rates have been simulated in a semiprognostic way and compared with the observations. The limitations of different schemes for numerical weather prediction are discussed. Among various Kuo-type cumulus parameterization schemes studied in this article, a modified Kuo-scheme is found to provide best results during the summer monsoon. In this scheme the moistening parameter is determined based upon the relative humidity and it is tuned for different phases of the monsoon. A comparison of the performance of various schemes during different phases of the monsoon was made. The heating and drying rates were best simulated during a preonset phase, when compared with the other two periods. The largest deviations between observed and simulated values were obtained during a break in the monsoon.